The present invention relates to electric arc furnace dust, and more particularly to methods and apparatus for processing electric arc furnace dust as a feedstock to recover iron and zinc value.
Electric Arc Furnace (EAF) dust is a waste material that is generated during the production of steel in electric arc furnaces. During the production of steel, EAF dust is captured and collected for either disposal or recycle.
The major components in EAF dust are iron (up to 50 wt %) and zinc (up to 30 wt %), usually in the oxide form. In addition, EAF dust contains smaller quantities of calcium, magnesium, manganese, chloride, lead, cadmium and other trace elements. The steel industry generates about 30 to 40 pounds of EAF dust for each ton of steel produced in electric arc furnace facilities. The estimated generation of EAF dust in the United States in 1997 was approximately 900,000 tons with about 40% being disposed in landfills.
EAF dust is a listed hazardous waste (K061) under United States environmental regulations. Under this regulatory program, EAF dust is subject to specific record keeping, handling requirements and processing costs when it is recycled or disposed.
However, EAF dust contains significant quantities of iron that make it valuable for use directly in steel making processes as a substitute for other iron containing materials such as scrap steel, hot metal, sinter dust, basic oxygen furnace (xe2x80x9cBOFxe2x80x9d) sludge and other iron oxides present at steel making facilities. In addition, EAF dust also contains significant quantities of zinc which makes it valuable as a feed for zinc manufacturing processes.
Present methods for handling EAF dust include processing it in Waelz Kilns, rotary hearth furnaces and flame reactor processes to recover zinc. EAF dust is also subject to stabilization processes followed by landfill disposal.
Generally, it can be economical to subject EAF dust having a high zinc content to existing zinc recovery procedures, and send EAF dust having a low zinc content to landfills for disposal as a waste.
Other process methods for recovering zinc and/or iron from EAF dust have been attempted with limited success. Such processes include thermal processes, hydrometallurgical processes or combinations thereof. In most cases these processes were not successful because they are expensive to build, expensive to operate and/or they cannot be used to process all of the EAF dust material, so that waste material remains that still must be disposed.
In addition, all processes are subject to significant environmental regulatory requirements under the Resource Conservation and Recovery Act (xe2x80x9cRCRAxe2x80x9d). This is due to the fact that current processes have been specifically developed for the sole purpose of processing EAF dust as a hazardous waste. To date, those in the steel industry view EAF dust as a listed hazardous waste, and accordingly conclude that using EAF dust as any type of feed or reactant will necessarily result in the formation, generation or preservation of a hazardous material.
Southwick, xe2x80x9cRecovery of Iron and Zinc From Steel Mill Wastes,xe2x80x9d a presentation from a Conference Organized by Gorham/Inertech in Pittsburgh. Pa. on May 17-19, 1999 provides a summary of various processes proposed to recover iron and zinc from mill wastes. In addition, U.S. Pat. Nos. 4,605,435, 5,013,532, 5,082,493, 5,435,835, 5,439,505, 5,493,580, 5,538,532, 5,667,553, 5,879,617, 5,993,512, 6,102,982, 6,120,577, and 6,221,124 are directed to various methods and apparatus for processing EAF dust.
The present invention is directed to methods and apparatus for processing electric arc furnace dust as a feedstock for a BOF.
According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a method of processing electric arc furnace dust as a feedstock which involves:
providing electric arc furnace dust from a source thereof;
providing a basic oxygen furnace;
feeding an iron containing material into the basic oxygen furnace;
feeding the electric arc furnace dust into the basic oxygen furnace together with the iron containing material; and
obtaining an iron product and a sludge/dust byproduct from the basic oxygen furnace.
The present invention further provides a method of recovering iron value from electric arc furnace dust which involves:
providing electric arc furnace dust;
providing a basic oxygen furnace;
feeding an iron containing material into the basic oxygen furnace;
feeding the electric arc furnace dust into the basic oxygen furnace together with the iron containing material so that iron oxide from the electric arc furnace dust is reduced and recovered in an iron product; and
removing the iron product and a sludge/dust byproduct from the basic oxygen furnace.
The present invention also provides for the combination of an electric arc furnace and a basic oxygen furnace for producing and processing electric arc furnace dust as a feedstock which combination includes:
an electric arc furnace;
a first feed of iron containing material going into the electric arc furnace;
an iron product and electric arc furnace dust obtained from the electric arc furnace;
a basic oxygen furnace; and
a feed or iron containing material and the obtained electric arc furnace dust going into the basic oxygen furnace;
an iron product and a sludge/dust byproduct obtained from the basic oxygen furnace.
According to one embodiment the combination further includes a zinc recovery system into which at least a portion of the obtained sludge/dust byproduct is feed as a feedstock.